The invention relates to internal combustion engines, and more particularly to a rotary valve system for such engines, the system being capable of varying timing and duration.
The basic structure and many advantages of rotary intake and exhaust valves for internal combustion engines are well known. The principal advantages are in the areas of maintenance and dependability, cost, ease of assembly, and engine size and weight.
In a typical internal combustion engine, engine efficiency is comprised by the provision of fixed valve timing and duration. This is true of conventional camshaft engines and also of typical rotary valve systems. The valve opening specification for a given engine is chosen for average engine load and speed conditions expected. A compromise thus results in that the engine is rendered much less efficient at differing engine conditions than would be the case if optimum valve settings could be employed for such differing conditions. Typically, valve overlap is too great at low engine r.p.m., and not sufficient at high r.p.m. and high engine loading, due to well known variations in the effects of charge momentum under varying conditions.
Various apparatus have been suggested for providing adjustable valve timing in connection with rotary valves. One such arrangement involves the use of blocking devices which may be added to or subtracted from the port opening leading into the valve rotor from either the intake or the exhaust manifold. Depending on the positioning of the blocking devices, the port may be modified to advance, retard, and/or modify the duration of the valve-open period. Of course this modification can only be made when the rotary valve assembly is dismantled.
Another suggested adjustable valve timing apparatus involves the use of an adjustable sleeve in the rotor housing in the position of the manifold side port. The sleeve, which includes an opening serving as the port, is circumferentially movable with respect to the valve rotor, so that the position of valve opening and closing can be varied and valve timing is accordingly adjusted. The timing can actually be adjusted during operation of the engine, in response to changing conditions, thereby somewhat broadening the optimum efficiency ranges of the engine in which the system is incorporated. However, besides presenting maintenance problems due to the complexity of the apparatus at the manifold side housing port, this type adjustable valve timing does not provide for adjustment of the duration of valve opening. Thus under conditions when it would be desirable to have a certain degree of valve overlap around top dead center piston position, and another degree of valve overlap around bottom dead center, these specific requirements cannot be met and engine efficiency is reduced.